1. Field of the Invention
The present invention relates to an image stabilizer provided in an optical instrument such as a camera, a pair of binoculars or the like, wherein the image stabilizer is provided with an image-stabilizing optical system which is driven to prevent the object image in the optical instrument from shaking due to hand movement.
2. Description of the Related Art
Optical instruments such as cameras, binoculars or the like which are provided with an image stabilizer having a vibration compensation function are well known. The image stabilizer is provided with an image-stabilizing optical system and operates to compensate the shaking of the object image (hereinafter referred to as xe2x80x9cimage shakexe2x80x9d) in the optical instrument by driving the image-stabilizing optical system in a plane perpendicular to the optical axis thereof.
The image-stabilizing optical system should be driven in a two-dimensional plane perpendicular to the optical axis. Therefore, if the image-stabilizing optical system slightly tilts with respect to the optical axis due to play, the focal point may deviate from the original position thereof. In practice, the clearance between the image-stabilizing optical system and the member or members which support and guide the image-stabilizing optical system cannot be made small enough to eliminate such play. Due to this reason, the image-stabilizing optical system is usually biased forwardly or rearwardly along the optical axis by a spring or springs to offset such play.
The image stabilizer can stabilize the object image only within a predetermined operable range of the image-stabilizing optical system, so that a movable limit position thereof in a direction perpendicular to the optical axis corresponds to the compensation limit position in the one direction. Generally, at the time the image-stabilizing optical system reaches a movable limit position thereof, the image-stabilizing optical system is controlled to stop electrically or stopped mechanically by a mechanical limit stop. However, due to a moment of inertia and the like, it is often the case that some drive force is still given to the image-stabilizing optical system even after it reaches to a compensation limit position. At this moment, the image-stabilizing optical system, which does not have any escape zone, undesirably tilts against the spring force of the aforementioned spring or springs.
Once such tilt occurs, several problems arise. Namely, the image-forming performance deteriorates, so that, e.g., the focal point deviates from the original position thereof. Moreover, the precision in detection of the position of the image-stabilizing optical system may deteriorate. In the case where the image stabilizer uses coils and permanent magnets to drive the image-stabilizing optical system, the electromagnetic force which is generated when current is supplied to one or more turns of wire positioned in magnetic field (i.e., the force represented by left-hand rule or Fleming""s rule) is utilized to drive the image-stabilizing optical system. However, since each coil itself generates magnetic field, magnetic attraction somewhat acts on the movement of the image-stabilizing optical system because of the positional relation between the coils and the permanent magnets, which also causes the image-stabilizing optical system to tilt.
The primary object of the present invention is to provide an image stabilizer which prevents the tilt of the image-stabilizing optical system, upon an image-stabilizing operation.
To achieve the object mentioned above, according to an aspect of the present invention, an image stabilizer is provided, including a movable member which supports an image-stabilizing optical system, a base which supports the movable member to be movable in a plane perpendicular to an optical axis of the image-stabilizing optical system, and at least three tilt prevention mechanisms, arranged on a circle centered on the optical axis, for preventing the image-stabilizing optical system from tilting at the time the image-stabilizing optical system reaches a movable limit position thereof in the plane perpendicular to the optical axis. Each of the at least three tilt prevention mechanisms includes a conically-tapered annular convex surface and a conically-tapered annular concave surface having an axis extending parallel to the optical axis, the conically-tapered annular convex surface and the conically-tapered annular concave surface being correspondingly formed on one and the other of the movable member and the base, respectively, so that the conically-tapered annular convex surface contacts the conically-tapered annular concave surface when the movable member reaches the movable limit position.
Preferably, each of the at least three tilt prevention mechanisms is arranged at an equi-angular distance therebetween about the optical axis.
Preferably, an outer diameter of the conically-tapered annular convex surface is smaller than an inner diameter of the conically-tapered annular concave surface.
In an embodiment, the movable member includes at least three projecting portions, arranged on a circle centered on the optical axis, each of the at least three projecting portions contacting with the base in a direction of the optical axis. The conically-tapered annular convex surface is provided on each of the at least three projecting portions.
In this embodiment, preferably, the base includes at least three plane circular surfaces with which the at least three projecting portions come into contact, respectively; and at least three ring-shaped protuberances which protrude towards the movable member from circumferences of the at least three plane circular surfaces, respectively. The conically-tapered annular concave surface is formed on an end surface of each of the at least three ring-shaped protuberances.
Each of the at least three projecting portions formed on the movable member can include a slidable member which is supported so as to be slidable in a direction parallel to the optical axis with respect to the movable member, and is continuously biased towards the base so as to contact the base. In this arrangement, the conically-tapered annular convex surface of the projecting portion is formed around the slidable member. In order to support the slidable member, for example, each of the at least three projecting portions includes a guide hole which extends in the direction of the optical axis, the slidable member being slidably fitted in the guide hole. A compression spring is provided in the guide hole, for biasing the slidable member towards the base.
In an embodiment, a support plate is further provided fixed to the base, and the movable member on which the at least three projecting portions are formed is positioned between the support plate and the base.
Each of the at least three projecting portions formed on the movable member can include a slidable member which is supported so as to be slidable in a direction parallel to the optical axis with respect to the movable member, and is continuously biased towards the support plate so as to contact the support plate. In this arrangement, the conically-tapered annular convex surface of the projecting portion is formed around the slidable member.
In an embodiment, the base includes at least three projecting portions, arranged on a circle centered on the optical axis, each of the at least three projecting portions contacting with the movable member in a direction of the optical axis, wherein the conically-tapered annular convex surface is provided on each of the at least three projecting portions.
In this embodiment, preferably, the movable member includes at least three plane circular surfaces with which the at least three projecting portions come into contact, respectively; and at least three ring-shaped protuberances which protrude towards the base from circumferences of the at least three plane circular surfaces, respectively. The conically-tapered annular concave surface is formed on an end surface of each of the at least three ring-shaped protuberances.
Each of the at least three projecting portions formed on the base can include a slidable member which is supported so as to be slidable in a direction parallel to the optical axis, and is continuously biased towards the movable member so as to contact the movable member. In this arrangement, the conically-tapered annular convex surface of the projecting portion is formed around the slidable member.
Further, the image stabilizer of the present invention can include a first drive device which drives the movable member in a first direction perpendicular to the optical axis; and a second drive device which drives the movable member in a second direction perpendicular to the optical axis, the first direction and second direction being orthogonal to each other.
The first drive device can include, for example, a first magnet fixed to one of the base and the movable member, and a first coil fixed to the other of the base and the movable member to face the first magnet, and the second drive device can include a second magnet fixed to the one of the base and the movable member, and a second coil fixed to the other of the base and the movable member to face the second magnet.
In an embodiment, the image stabilizer further includes first and second gyro sensors for sensing vibration in the first direction and the second direction, respectively; and a controller which supplies drive current to each of the first coil and the second coil, wherein the strength of the drive current is determined in accordance with output of each of the first and second gyro sensors.
The image stabilizer can be incorporated in a camera. Furthermore, the image stabilizer can be formed as a unit.
According to another aspect of the present invention, an image stabilizer is provided, including a movable member which supports an image-stabilizing optical system, a base which supports the movable member to be movable in a plane perpendicular to an optical axis of the image-stabilizing optical system, and a tilt prevention device for preventing the image-stabilizing optical system from tilting at the time the image-stabilizing optical system reaches a movable limit position thereof in the plane perpendicular to the optical axis. The tilt prevention device includes at least three tilt prevention mechanisms arranged on a circle centered on the optical axis at an equi-angular distance therebetween about the optical axis.
Preferably, each of the at least three tilt prevention mechanisms is arranged at an equi-angular distance therebetween about the optical axis.
Each of the three tilt prevention mechanisms can include, for example, a conically-tapered annular convex surface and a conically-tapered annular concave surface formed on one and the other of the movable member and the base, respectively, each of the conically-tapered annular convex surface and the corresponding conically-tapered annular concave surface having an axis extending parallel to the optical axis. When the image-stabilizing optical system reaches the movable limit position thereof in the plane perpendicular to the optical axis, the conically-tapered annular convex surface and the conically-tapered annular concave surface, of each of the tilt prevention mechanism, contact each other so that tilting of the movable member with respect to the base is prevented.
The present disclosure relates to subject matter contained in Japanese Patent Application No.11-141200 (filed on May 21, 1999) which is expressly incorporated herein by reference in its entirety.